Composite polyamido reverse osmosis (RO) membranes are known. See, for example, U.S. Pat. Nos. 4,259,183, 4,529,646, 4,277,344 and 4,039,440. However, there is still a need in the RO art for high flux membranes that are resistant to attack by halogens such as chlorine, often present in brackish feed waters. The present invention comprises a novel RO membrane having a "loose" molecular structure that exhibits extraordinarily high flux and high resistance to chlorine attack.